The invention relates to exhaust systems for marine propulsion devices, and, more particularly, to low-speed exhaust systems for marine propulsion devices.
Marine propulsion device exhaust gases are typically discharged underwater, with the exhaust gases flowing downwardly through the lower unit and then out through the propeller. At relatively high boat speeds, a low pressure region exists behind the propeller and exhaust gases are easily discharged through the propeller. At engine idle or relatively low boat speeds, water backs up into the exhaust gas passageway and creates a back pressure which restricts or prevents the discharge of exhaust gases through the propeller.
Exhaust systems have been provided for discharging exhaust gases through a discharge outlet located above the water when the engine is operating at relatively low speeds. Examples of such systems are disclosed in U.S. Wenstadt patent application No. 754,534, filed July 12, 1985, U.S. Binversie et al. patent application No. 058,365, filed June 4, 1987, and U.S. Broughton et al. patent application No. 062,435, filed June 12, 1987, all of which are assigned to the assignee of this application.
Attention is also directed to the following U.S. Patents:
______________________________________ Patentee U.S. Pat. No. Issue Date ______________________________________ Hulsebus 3,045,423 July 24, 1962 Larsen 3,198,162 August 3, 1965 Gazzara 3,282,373 November 1, 1966 Hoiby et. al. 3,296,997 January 10, 1967 Kollman 3,310,022 March 21, 1967 Boda et al. 3,350,879 November 7, 1967 Miller 3,520,270 July 14, 1970 Tado 3,577,952 May 11, 1971 Miller et al. 3,911,852 October 14, 1975 Harralson et al. 3,967,446 July 6, 1976 Maier et al. 4,036,162 July 19, 1977 Harbert 4,019,456 April 26, 1977 Harada 4,145,988 March 27, 1979 Sanmi et al. 4,303,401 December 1, 1981 Sanmi et al. 4,354,849 October 19, 1982 Nakahama 4,421,490 December 20, 1983 Hall et al. 4,507,092 March 26, 1985 Price 4,589,852 May 20, 1986 Taguchi 4,604,069 August 5, 1986 Okazaki 4,607,723 August 26, 1986 Freund et al. 4,668,199 May 26, 1987 ______________________________________
Attention is also directed to the following Japanese patent applications: Application No. 54-25059, filed Mar. 6, 1979; Application No. 55-133541, filed Sept. 25, 1980; Application No. 55-155500, filed Nov. 5, 1980; Application No. 55-156562, filed Nov. 7, 1980; and Application No. 57-68908, filed Apr. 24, 1982.